1. Technical Field
The present invention relates to wireless communications, and more particularly, to a method of scheduling transmission/reception of messages relating to multimedia broadcast/multicast service (MBMS).
2. Related Art
Multimedia Broadcast and Multicast Services (MBMS) correspond to broadcasting services which can be offered in GSM and UMTS cellular networks. Such services can be mobile TV services for instance.
All UEs (‘User Equipment’ or terminal), supporting MBMS, receive MBMS information (‘MI’) from UTRAN (‘UMTS Terrestrial Radio Access Network’) concerning the way MBMS services provided in their location. Most of MBMS information is provided on the MCCH channel. The MCCH channels are used as downlink point-to-multipoint downlink channels to transmit this MCCH information. In general, one cell has one corresponding MCCH.
This MBMS information on MCCH channel is transmitted using a fixed schedule, which is common for all services. Most of MCCH information is transmitted periodically based on a repetition period. This MCCH information is repeated a configurable number of times with exactly the same content. The time period in which the content of this MCCH information remains unchanged is called the ‘modification period’.
MCCH information can be modified in a modification period, more precisely, at the beginning of the modification period. Moreover, inside one modification period, the MCCH information is repeated according to the repetition period.
Then, MCCH information sent periodically can contain both Unmodified Service Information (USI), repeating control information which are not modified for a service, and Modified Service Information (MSI), indicating control information modified for a service. After a time, MSI is considered as unmodified and then it is included in USI.
According to this MCCH information transmission scheduling, it can be noted that the transmission of MCCH information could be not useful. Actually, for instance, it is not useful for a UE to receive often USI, except in the following situations: when a radio link failure occurs between the network and the UE, and when the mobility of the UE makes it to change of service areas.
For instance, in LTE (‘Long Term Evolution’) architecture, a plurality of MBSFN areas (‘Multi-Media Broadcast over a Single Frequency Network’) can be defined, each MBSFN area having one MCCH channel to transmit MCCH information to all UEs in said MBSFN area. In these conditions, because of mobility, a UE could be located in another MBSFN area and consequently it will receive MCCH information on another MCCH channel. In this case, the UE must receive all MCCH information including MSI and USI to be able to receive service inside the MBSFN area where it is located now.
But, in general, when the radio link is reliable and the UE does not move enough to change its MBSFN area, it could be not very useful to receive often the USI.
It is important to note that a transmission of not useful information generates overhead.
Accordingly, there is a need for a method of effectively transmitting MCCH information in a MBMS system.